Hybrid organic-inorganic materials consist of inorganic (e.g. oxides) and organic (e.g. small molecules, macromolecules, etc.) components. They benefit from the thermal and chemical stability and strength of inorganic components (e.g. oxides), while exhibiting the elasticity and functionality of organic molecules. Due to the synergistic advantages, many research groups have attempted to develop novel hybrid materials with enhanced properties by carefully designing the chemical composition and controlling structure growth.
Bridged polysilsesquioxanes (BPS) (Shea, K. J.; Loy, D. A. Chem. Mate, 2001, 13, 3306-3319. (b) Shea, K. J.; Loy, D. A.; Webster, 0. 1 J. Am. Chem. Soc. 1992, 114, 6700-67 10; herein incorporated by reference in their entireties) are materials with silicon-oxide networks and organic bridging groups. Synthesized with sol-gel chemistry from organo-bridged bis-trialkoxysilanes ((R′O)3Si—R—Si(OR′)3) the organic and inorganic domains in the material are dispersed at the molecular level. The organic group provides an opportunity to control bulk properties such as refractive index, optical clarity, hydrophobicity, dielectric constant, thermal stability and chemical function. Moreover, compared to organic modified ceramics (ORMOCER®) synthesized from R—Si(OR)3, the organic bridging group in BPS, serving as a spacer between two Si—O linkage groups, often provide significant and well-modulated porosity, allowing the use of “inner surfaces” (up to ˜1000 m2/g) of materials.
Recent developments for preparing functional materials as spherical microparticles and/or nanoparticles have broadened the potential applications and enhanced the performance of these materials significantly. Small, uniform spherical particles are widely used in separations, for drug and gene delivery (Barbe et al. Adv. Mater 2004, 16, 1959-1966.; Singh et al. Proc. Nat. Acaci Sci. USA. 2000, 97, 811-816.; Roy et al. Proc. Nat. Acad. Sci. USA. 2005, 102, 279-284.; Bharali et al. Proc. Nat. Acad. Sci. USA. 2005, 102, 11539-11544.; Roy et al. J. Am. Chem. Soc. 2003, 125, 7860-7865.; Wang et al. Nat. Mater 2004, 3,190-196.; Sengupta et al. Nature 2005, 436, 568-572.; Haag. Angew. Chem. mt. Ed 2004, 43, 278-282.; Yoon et al. Angew. Chem. In,’. Ed 2005, 44, 1068-1071.; Yan et al. Adv. Mater 2006, 18, 2373.; herein incorporated by reference in their entireties), bioimaging (Santra et al. Adv. Mater 2005, 17, 2165-2169.; Lee et al. J. Angew. Chem. mt. Ed. 2006, 45, 8160-8162.; herein incorporated by reference in their entireties), catalysis (Beydoun et al. Nanopart. Res. 1999, 1, 439-458; Zhong et al. Adv. Mater 2001, 13, 1507.; herein incorporated by reference in their entireties), and for optical (Zhu et al. J. Am. Chem. Soc. 2006, 128, 4303-4309.; Ow et al. Nano Lett. 2005, 5, 113-117.; herein incorporated by reference in their entireties), electronic (Kaltenpoth et al. Adv. Mater 2003, 15, 1113-1118.; Jang et al. Adv. Mater 2005, 17, 1382-1386.; herein incorporated by reference in their entireties), and magnetic (Yi et al. Chem. Mater 2006, 18, 614-619.; Lu et al. Angew. Chem. mt. Ed 2007, 46, 1222-1244.; Toprak et al. Adv Mater 2007, 19, 1362.; Ma et al. Polym. Sci., Part A: Polym. Chem 2005, 43, 3433-3439.; Xu et al. J. Am. Chem. Soc. 2006, 128, 15582-15583.; Lu et al. Nano Lett. 2007, 7, 149-154.; herein incorporated by reference in their entireties) applications. Recently, BPS were also prepared as xerogel nanoparticles by self-assembly or in a variety of emulsion methods (Khiterer, M.; Shea, K. J. Nano Lett. 2007, 7, 2684-2687; herein incorporated by reference in its entirety). These nanoparticles can be used as photodeformable materials or components in electrochromic devices. However, the emulsion method is suitable only when water-in-oil emulsions are used for ionic and water soluble monomers. Hydrophobic monomers become amphiphilic after hydrolysis, thus not constrained in micelles. Since most of bridged silane monomers are water-insoluble, new methods are needed in the field to prepare BPS in uniform, spherical particles.
The Stöber process, first reported in 1968 (Stober et al. Colloid Interface Sci. 1968, 26, 62-69.; herein incorporated by reference in its entirety), yields monodisperse spherical non-porous silica particles by the hydrolysis and condensation of Si(OEt)4 in mixtures of ammonia, alcohol and small amounts of water. ORMOSIL particles can be prepared by a method similar to the Stöber process (Choi et al. J. Am. Ceram. Soc. 1998, 81, 1184-1188.; Katagiri et al. J. Am. Ceram. Soc. 1998, 81, 2501-2503.; Matsuda et al. J. Sol-Gel Sd. Technol. 2002, 23, 247-252.; Liu et al. Eur: Polym. 1 2005, 4), 996-1001.; Arkhireeva & Hay, J. Mater Chem. 2003, 13, 3122-3127.; Arkhireeva et al. J. Sol-GeiSci. Technol. 2004, 31, 31-36.; herein incorporated by reference in their entireties), in which aqueous ammonium hydroxide (without alcohol) is used as solvent. During the reaction, the monomer “oil droplets” are gradually consumed, while a turbid suspension of organic-silica particles emerges in the aqueous phase.